The present invention is a method to provide a lubricant layer to an imaging element. More particularly the present invention eliminates the use of solvent in applying the lubricant layer to an imaging element.
Photographic and image or information recording media require adequate lubrication for the purposes of transport through recording devices and imaging devices (camera, photofinishing, thermal head, etc.), and for scratch protection. Also, backing layers on photographic negative film that can be used to magnetically record, and subsequently, to retrieve, information require excellent lubrication at their surface to improve the durability of the recording layer. Contact between the magnetic head and the outermost surface of the backing layers of the film is necessary, however, this imposes a great amount of stress to the backing layers and may result in rupture of the layer, and in loss of signal. Good lubrication allows for multiple transports of the film through various magnetic head-containing equipment. The lubricant must also remain effective after the film has been run through photographic processing solutions.
Polyethylenes, silicone waxes, natural waxes such as Carnauba, polytetrafluoroethylene (PTFE), and fluorinated ethylene propylene (FEP) are known to be lubricating agents. Some are not soluble, some are soluble in limited solvents which impose constraints and difficulties for the coating of these lubricants and on manufacturing. In addition, the solvents used as vehicles for the wax may attack or cause damage or undesirable changes in the surface of the layer or layers onto which the lubricant is being coated. In addition, these carrier solvents may not be environmentally friendly.
Imaging elements containing transparent magnetic oxide coatings on the side opposite the imaging emulsions have been well-documented. The need for lubricating layers on said magnetic oxide coatings have also been well-described. A variety of types of lubricants have been disclosed including fatty acids, fatty acid esters, silicones, waxes, etc. In general, the transparent magnetic layer and the lubricating layer are applied in separate coating steps. This reduces the manufacturing efficiency of the product by requiring several coating stations. Typically these layers have been applied by first coating a solution of the magnetic oxide layer onto a support using a bead coating technique. The coating is then dried and a lubricant layer is then coated over the magnetic layer using a similar technique. Thus, another disadvantage is that the lubricant containing layer is typically applied using a solvent as a carrier, thus, generating solvent and solvent vapor waste.
Alternatively, the lubricant can be added to the magnetic oxide coating solution such that both the magnetics and lubricant arc coated simultaneously. This is advantageous because less coating stations are required, likely reducing waste and simplifying the production. Unfortunately, in order for the lubricant to be effective it must primarily reside at the uppermost surface of the dry coating. When the lubricant is added to the magnetic oxide solution, it is difficult for the lubricant to get to the surface. As the solution dries rapidly, the polymeric binder for the magnetic oxide will vitrify or solidify, which retards the mobility of the lubricant. Additionally, the lubricant may also go to the support/magnetics interface instead of the desired magnetics/air interface. The result is an improperly lubricated surface, or a coating with a high coefficient of friction.
Another drawback of adding the lubricant directly to the magnetics layer is that phase separation can occur resulting in a translucent or opaque film. The lubricant can destabilize the magnetics dispersion, resulting in flocculation of the particles. Also, the lubricant may not be compatible with the magnetics binder, which can lead to gross phase separation and loss of optical transparency. It is desired to have the lubricant phase separate and migrate to the air interface, without the loss of optical transparency. Obviously a very selective phase separation is desired and is difficult to control. Alternatively, the lubricant may not be soluble, or dispersible in the same solvents as are needed for the components of the transparent magnetic layer.
Japanese Patent1251349 A (New Nippon Electric Co) discusses a magneto-optical recording medium that comprises an optically transparent substrate onto which a magnetic film is formed. A macromolecular film formed by plasma polymerization of tetrafluoroethylene monomer is formed on the surface-side dielectric substance film. Vacuum deposition of PTFE-like substances involve starting with gaseous monomers and doing a plasma polymerization. The present invention offers the advantage that the original lubricant materials are preformed polymers as opposed to monomers such as tetrafluoroethylene, thus avoiding complex handling of often toxic gases. In addition, exposing the surface to the plasma can degrade the magnetic and underlying layers and compromise the coefficient of friction, the durability, and the abrasion resistance of the element.
U.S. Pat. No. 4,863,762 describes a physical vapor deposition technique that deposits fluororesins onto a surface. However, in this process, there is a need to degrade the molecular weight of the initial resin sample prior to the vacuum deposition process. This is done by heating the resin in the presence of a fluorine source. U.S. Pat. No. 4,390,601 describes the vacuum deposition of a lubricant onto a (non-transparent) magnetic substrate. The lubricants described are paraffins, fatty-acids and soaps, which are not the subject of the present application. The deposition process described is for a stationary substrate, not a moving web.
What is needed in the art is a method that does not require solvents, does not require a solvent coating machine, and also ensures that the lubricant remains at the outermost surface of the transparent magnetic layer. Thus a manufacturing advantage would be obtained since a solvent coating machine would not be required for the application of this lubricant, which offers capacity advantages. Also, environmental benefits would be obtained due to the elimination of solvent waste and evaporation. A minimal amount of lubricant would be deposited by this method, so that lube transfer to the head would be minimized and head clogging problems reduced.
The present invention describes a means of obtaining a lubricated layer on an imaging element via deposition of the lubricant onto a dried magnetic layer via an evaporative process. The method includes providing a polymer or a wax selected from the group consisting of polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), fluorinated ethylene copolymers, polyethylenes, high density polyethylene, natural waxes such as Carnauba wax, synthetic waxes, and silicone waxes in a deposition chamber. The chamber is evacuated to a pressure of 10 xe2x88x921 Torr or less A carrier gas is bled into the chamber while maintaining the pressure in the chamber to 100 mTorr or less. Preferred gases are selected from the group consisting of N2, O2, and Ar. The polymer or wax is heated to a temperature sufficient to vaporize the polymer or wax, and the imaging element is moved through the chamber on a continuously moving web, depositing the polymer or wax on the imaging element to form the lubricating layer.
The present invention provides low coefficient of friction and, in addition, provides durability for excellent performance under a magnetic head. The lubricant layer is transparent and does not interfere with the transmission of light through the imaging element.
A support, coated with appropriate layers (e.g. subbing, antistat, and transparent magnetic oxide layers) on the side opposite to the emulsion layers, is exposed, under vacuum, to a lubricant vapor phase. The lubricant vapor phase is obtained by heating the material to high enough temperatures to produce evaporation, or partial chemical breakdown, followed by evaporation. An appropriate background gas (such as argon, nitrogen, oxygen, etc.) is used to maintain a controlled atmosphere for the lubricant vapor phase to pass through as it deposits on the web. The side of the support that is coated with the vaporized lubricant is the side opposite to the emulsion layers.
Typical conditions for the deposition of the lubricant are a pressure of between 10-1000 mT, preferably 100 mT and a temperature within the range of 300xc2x0 C. to 660xc2x0 C. The support continuously moves through the chamber at a speed of between 1 and 1000 feet per minute. The temperature of evaporation that is chosen depends on the melting point of the lubricant and on the speed of the moving support. Any carrier gas can be used, most typical gases are Nitrogen, Argon, or Oxygen.
Any typical wax or known solid or waxy lubricant can be used for this invention. In particular, typical lubricants include polyethylenes, high density polyethylene, silicone waxes, natural waxes such as Carnauba, synthetic waxes, polytetrafluoroethylene, fluorinated ethylene propylene, and fluorinated ethylene copolymers.
The base support for the present invention can be cellulose derivatives such as a cellulose ester, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, polyesters, such as polyethylene terephthalate or polyethylene naphthalate, poly-1,4-cyclohexanedi-methylene terephthalate, polybutylene terephthalate, and copolymers thereof, polyimides, polyamides, polycarbonates, polystyrene, polyolefins, such as polyethylene, polypropylene, polysulfones, polyarylates, polyether imides and blends of these. The support typically employs an undercoat or a subbing layer well known in the art that comprises, for example, for a polyester support a vinylidene chloride/methyl acrylate/itaconic acid terpolymer or a vinylidene chloride/acrylonitrile/acrylic acid terpolymer.
The imaging elements according to this invention can contain one or more conducting layers such as antistatic layers and/or antihalation layers such as described in Research Disclosure, Vol. 176, December 1978, Item 17643 to prevent undesirable static discharges during manufacture, exposure and processing of the photographic clement. Antistatic layers conventionally used for color films have been found to be satisfactory herewith. Any of the antistatic agents set forth in U.S. Pat. No. 5,147,768 which is incorporated herein by reference may be employed. Preferred antistatic agents include metal oxides, for example tin oxide, antimony doped tin oxide and vanadium pentoxide. These antistatic agents are preferably dispersed in a film forming binder.
The magnetic particles in the transparent magnetic layer can be ferromagnetic iron oxides, such as xcex3-Fe2O3, xcex3-Fe3O4, xcex3-Fe2O3 or Fe3O4 with Co, Zn or other metals in solid solution or surface treated or ferromagnetic chromium dioxides, such as CrO2 with metallic elements, for example Li, Na, Sn, Pb, Fe, Co, Ni, and Zn, or halogen atoms in solid solution. Ferromagnetic pigments with an oxide coating on their surfaces to improve their chemical stability or dispersability, as is commonly used in conventional magnetic recording, may also be used. In addition, magnetic oxides with a thicker layer of lower refractive index oxide or other material having a lower optical scattering cross-section as taught in U.S. Pat. Nos. 5,217,804 and 5,252,444 can be used. These are present in the transparent magnetic layer in the amount from about 1 to 10 weight percent based on the weight of the binder. The magnetic particles have a surface area greater than 30 m2/gm and a coverage of from about 1*10xe2x88x9211 mg/xcexcm3 to 1*10xe2x88x9210 mg/xcexcm3. A dispersing agent, or wetting agent can be present to facilitate the dispersion of the magnetic particles. This helps to minimize the agglomeration of the magnetic particles. Useful dispersing agents include fatty acid amines and commercially available wetting agents such as Witco Emcol(trademark) CC59 which is a quaternary amine available from Witco Chemical Corp. Rhodafac(trademark) PE 510, Rhodafac(trademark) RE 610, Rhodafac(trademark) RE960, and Rhodafac(trademark) LO0529, which are phosphoric acid esters available from Rhone-Poulenc.
The polymer binder of the transparent magnetic layer may be any polymer having good abrasion resistance. For example, cellulose esters such as cellulose diacetates and triacetatos, cellulose acetate propionate, cellulose acetate butyratc, cellulose nitrate, polyacrylates such as polymethyl methacrylate, polyphenylmethacrylate and copolymers with acrylic or methacrylic acid, or sulfonates, polyesters, polyurethanes, urea resins, melamine resins, urea-formaldehyde resins, polyacetals, polybutyrals, polyvinyl alcohol, epoxies and epoxy acrylates, phenoxy resins, polycarbonates, vinyl chloridc-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl-alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid polymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, acrylic ester-acrylonitrile copolymers, acrylic ester-vinylidene chloride copolymers, methacrylic ester-styrene copolymers, butadiene-acrylonitrile copolymers, acrylonitrile-butadiene-acrylic or methacrylic acid copolymers, styrene-butadiene copolymers can be used as binders in the transparent magnetic layer. Cellulose ester derivatives, such as cellulose diacetates and triacetates, cellulose acetate propionate, cellulose nitrate, polyesters, and polyacrylates such as polymethyl methacrylate, polyphenylmethacrylate and copolymers with acrylic or methacrylic acid are preferred.
Abrasive particles useful in the magnetic layer include nonmagnetic inorganic powders with a Mohs scale hardness of not less than 6. These include, for example, metal oxides such as alpha-alumina, chromium oxide (Cr2O3), alpha-Fe2O3, silicon dioxide, alumino-silicate and titanium dioxide. Carbides such as silicone carbide and titanium carbide, nitrides such as silicon nitride, titanium nitride and diamond in fine powder may also be used. Alpha alumina and silicon dioxide are preferred. These are included to improve the head cleaning properties and improve durability of the coating. A dispersing agent, or wetting agent can be present to facilitate the dispersion of the abrasive particles. This helps to minimize the agglomeration of the particles. Useful dispersing agents include, but are not limited to, fatty acid amines and commercially available wetting agents such as Solsperse(trademark) 24000 sold by Zeneca, Inc. (ICI). The abrasive particles have a median diameter of about 0.2 to 0.4 xcexcm. The abrasive particles are present in the magnetic layer in die amount of at least 2 weight percent based on the weight of the binder so that durability of the coating is achieved and clogging of the magnetic heads is prevented. The upper limit of the amount of abrasive particles is determined by the loss of transparency of the layer, adversely affecting the photographic element, and by their abrasive effects on the magnetic heads and the tools and photographic apparatus that the film comes in contact with, leading to premature wear of these tools and apparatus. Typically, the abrasive particles are present in the transparent magnetic layer in the amount of 2 wt % to about 20 wt % relative to the weight of the binder.
Filler particles useful in the magnetic layer have a median diameter less than 0.15 xcexcm, preferably less than 0.1 xcexcm. The filler particles have a Mohs hardness greater than 6 and are present in the amount from about 0 to 300 percent, most preferably in the amount from about 0 to 85 percent based on the weight of the binder. Examples of filler particles include nonmagnetic inorganic powders such as xcex4-aluminum oxide, chromium oxide, iron oxide, tin oxide, doped tin oxide, silicon dioxide, alumino-silicate, titanium dioxide, silicon carbide, titanium carbide, and diamond in fine powder, as described in U.S. Pat. No. 5,432,050. A dispersing agent, or wetting agent can be present to facilitate the dispersion of the filler particles. This helps to minimize the agglomeration of the particles. Useful dispersing agents include, but are not limited to, fatty acid amines and commercially available wetting agents such as Solsperse(trademark) 24000 sold by Zeneca, Inc. (ICI). Preferred filler particles are gamma-aluminum oxide and silicon dioxide.
The transparent magnetic layer may include coating aids and surfactants such as nonionic fluorinated alkyl esters such as FC-430, FC-431, FC-10, FC171 sold by Minnesota Mining and Manufacturing Co., Zonyl fluorochemicals such as Zonyl-FSN(trademark), Zonyl-FTS(trademark), Zonyl-TBS(trademark), ZonylBA(trademark) sold by DuPont; polysiloxanes such as Dow Coming DC 1248, DC200, DC510, DC 190 and BYK 320, BYK 322, sold by BYK Chemic and SF 1079, SF1023, SF 1054, and SF 1080 sold by General Electric; polyoxyethylene-lauryl ether surfactants sold by Kodak; sorbitan laurate, palmitate and stearates such as Span surfactants sold by Aldrich.
Viscosity modifiers can be present in the transparent magnetic layer. Such viscosity modifiers include high molecular weight cellulose esters, cellulosics, acrylics, urethanes, and polyethylene oxides.
Solvents useful for coating the transparent magnetic layer of the present invention include alcohols, ketones, acetates, chlorinated solvents, esters, water, hydrocarbons, ethers, or mixtures thereof.
In an embodiment of this invention, the imaging element is a thermal dye diffusion receiving element that can be transparent or opaque. In another embodiment of this invention, the imaging element is a thermal dye diffusion dye donor element. In another embodiment of this invention, the imaging element is an inkjet ink receiving element that can be transparent or opaque.
In a particularly preferred embodiment, the imaging elements of this invention are photographic elements, such as photographic films, photographic papers or photographic glass plates, in which the image-forming layer is a radiation-sensitive silver halide emulsion layer. Such emulsion layers typically comprise a film-forming hydrophilic colloid. The most commonly used of these is gelatin and gelatin is a particularly preferred material for use in this invention. Useful gelatins include alkali-treated gelatin (cattle bone or hide gelatin), acid-treated gelatin (pigskin gelatin) and gelatin derivatives such as acetylated gelatin, phthalated gelatin and the like. Other hydrophilic colloids that can be utilized alone or in combination with gelatin include dextran, gum arabic, zein, casein, pectin, collagen derivatives, collodion, agar-agar, arrowroot albumin, and the like. Still other useful hydrophilic colloids are water-soluble polyvinyl compounds such as polyvinyl alcohol, polyacrylamide, poly(vinylpyrrolidone), and the like.
The photographic elements of the present invention can be simple black-and-white or monochrome elements comprising a support bearing a layer of light-sensitive silver halide emulsion or they can be multilayer and/or multicolor elements.
Color photographic elements of this invention typically contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single silver halide emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as is well known in the art.
A preferred photographic element according to this invention comprises a support bearing at least one blue-sensitive silver halide emulsion layer having associated therewith a yellow image dye-providing material, at least one green-sensitive silver halide emulsion layer having associated therewith a magenta image dye-providing material and at least one red-sensitive silver halide emulsion layer having associated therewith a cyan image dye-providing material.
In addition to emulsion layers, the photographic elements of the present invention can contain one or more auxiliary layers conventional in photographic elements, such as overcoat layers, spacer layers, filter layers, interlayers, antihalation layers, pH lowering layers (sometimes referred to as acid layers and neutralizing layers), timing layers, opaque reflecting layers, opaque light-absorbing layers and the like. The support can be any suitable support used with photographic elements. Typical supports include polymeric films, paper (including polymer-coated paper), glass and the like. Details regarding supports and other layers of the photographic elements of this invention are contained in Research Disclosure, Item 36544, September, 1994.
The light-sensitive silver halide emulsions employed in the photographic elements of this invention can include coarse, regular or fine grain silver halide crystals or mixtures thereof and can be comprised of such silver halides as silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chorobromoiodide, and mixtures thereof. The emulsions can be, for example, tabular grain light-sensitive silver halide emulsions. The emulsions can be negative working or direct positive emulsions. They can form latent images predominantly on the surface of the silver halide grains or in the interior of the silver halide grains. They can be chemically and spectrally sensitized in accordance with usual practices. The emulsions typically will be gelatin emulsions although other hydrophilic colloids can be used in accordance with usual practice. Details regarding the silver halide emulsions are contained in Research Disclosure, Item 36544, September, 1994, and the references listed therein.
The photographic silver halide emulsions utilized in this invention can contain other addenda conventional in the photographic art. Useful addenda are described, for example, in Research Disclosure, Item 36544, September, 1994. Useful addenda include spectral sensitizing dyes, desensitizers, antifoggants, masking couplers, DIR couplers, DIR compounds, antistain agents, image dye stabilizers, absorbing materials such as filter dyes and UV absorbers, light-scattering materials, coating aids, plasticizers and lubricants, and the like.
Depending upon the dye-image-providing material employed in the photographic clement, it can be incorporated in the silver halide emulsion layer or in a separate layer associated with the emulsion layer. The dye-image-providing material can be any of a number known in the art, such as dye-forming couplers, bleachable dyes, dye developers and redox dye-releasers, and the particular one employed will depend on the nature of the clement, and the type of image desired.
Dye-image-providing materials employed with conventional color materials designed for processing with separate solutions are preferably dye-forming couplers; i.e., compounds which couple with oxidized developing agent to form a dye. Preferred couplers which form cyan dye images are phenols and naphthols. Preferred couplers which form magenta dye images arc pyrazolones and pyrazolotriazoles. Preferred couplers which form yellow dye images are benzoylacetanilides and pivalylacetanilides.
The present invention is illustrated by the following examples.